Location tracking using fiber optic array cables and related systems and methods

ABSTRACT

Fiber optic array cables and related systems and methods to determine and/or track locations of objects are disclosed. The fiber optic array cables can be employed in an optical-fiber-based communication system, including a centralized optical-fiber based communication system. In one embodiment, the fiber optic array cable is configured to carry optical RF or radio-over-fiber (RoF) signals to establish communications with objects. The fiber optic array cable includes multiple reference units along the length of the cable. The reference units can be configured to convert received optical RF signals into electrical RF signals to establish RF communications with objects capable of receiving electrical RF signals. The reference units are also configured to convert received electrical RF signals from the objects into optical RF signals, which are then used to determine the location of the object. Having the availability of the multiple reference units on one or more the fiber optic array cables can provide enhanced reliability in tracking objects.

This application is a continuation of U.S. patent application Ser. No.12/509,099, filed Jul. 24, 2009, the content of which is herebyincorporated herein by reference in its entirety, and the benefit ofpriority under 35 U.S.C §120 is hereby claimed.

BACKGROUND

Field of the Disclosure

The technology of the disclosure relates generally to wirelesscommunication systems, and more particularly to optical-fiber-basedwireless cables, systems, and methods.

Technical Background

Wireless communication is rapidly growing, with ever-increasing demandsfor high-speed mobile data communication. As an example, “wirelessfidelity” or “WiFi” systems and wireless local area networks (WLANs) arebeing deployed in many different types of areas (office buildings,airports, libraries, etc.). Wireless communication systems communicatewith wireless devices called “clients,” which reside within the wirelessrange or “cell coverage area” to communicate with the access pointdevice.

One approach of deploying a wireless communication system involves useof “picocells.” Picocells are radio-frequency (RF) coverage areas.Picocells can have a radius in the range from a few meters up to twentymeters as an example. Combining a number of access point devices createsan array of picocells that cover an area called a “picocellular coveragearea.” Because each picocell covers a small area, there are typicallyonly a few users (clients) per picocell. This allows for simultaneoushigh coverage quality and high data rates for the wireless system users.

One advantage of picocells is the ability to wireless communicate withremotely located communication devices within the picocellular coveragearea. It may also be desirable to determine and/or track the location ofsuch devices within the picocellular coverage area.

SUMMARY OF THE DETAILED DESCRIPTION

Embodiments disclosed in the detailed description include fiber opticarray cables and related systems and methods. Such cables, systems, andmethods can be employed to determine and/or track the location of anobject. The fiber optic array cable can be employed in anoptical-fiber-based communication system, including but not limited to acentralized optical-fiber-based communication system. In one embodiment,the fiber optic array cable includes multiple reference units along thelength of the cable. Each reference unit in the fiber optic array cablecan include an antenna, and an electrical-to-optical (E/O) converter,and an optical-to-electrical (O/E) converter to convert electrical RFsignals to optical RF signals, and vice versa, respectively. Thereference units can be configured to convert received optical RF signalsinto electrical RF signals to establish RF communications with objectscapable of receiving electrical RF signals. The reference units can alsobe configured to convert received electrical RF signals from the objectsinto optical RF signals, which are then used to determine the locationof the object.

Having the availability of the multiple reference units on one or morethe fiber optic array cables can provide enhanced reliability intracking objects, including objects in an indoor environment. Themultiple reference units of the fiber optic array cables disclosedherein can increase the probability of having sufficient communicationpaths to the object being tracked. Further, providing the multiplereference units in a fiber optic array cable allows the use of opticalfiber as a transmission medium for communications to the trackedobjects. The fiber optic array cables may be provided such that remoteobjects can be tracked using optical fiber communications with highbandwidth speeds.

According to one embodiment disclosed herein, RF signals, such asUltraWideBand-Impulse Radio (UWB-IR) signals for example, can betransmitted over the fiber optic array cables to determine and/or trackthe location of the object. Systems using UWB-IR signals in particular,although not limiting herein, can provide accurate ranging capability.The accurate ranging capability of UWB-IR systems does not deterioratewhen UWB-IR signals are transmitted over a centralized RoF system. Thus,by transmitting UWB-IR signals over a centralized optical-fiber-basedcommunication system that includes one or more fiber optic array cableshaving multiple reference units, accurate and reliable three-dimensionaltracking of a target object can be enabled.

Other embodiments disclosed in the detailed description provide acentralized optical-fiber-based wireless communication system thatincorporates one or more of the fiber optic reference array cableshaving multiple reference units disposed along a length of the fiberoptic cable. Each of the multiple reference units comprises at least oneantenna, an E/O converter, and an O/E converter. In this regard, each ofthe reference units may form one or more picocells. The centralizedoptical-fiber-based wireless communication system includes a centralhead-end station having a plurality of service units and at least onefiber optic reference array cable remote from the central head-endstation. An electrical power line extends from the central head-endstation to provide power to the E/O converter and the O/E converter. Aservice unit in the central head-end station is configured to cause anRF signal, such as an UWB signal, to be transmitted from one or more ofthe antennas in the multiple reference units to a wireless coverage areaassociated with the reference unit. A corresponding signal is receivedfrom one or more of the plurality of the multiple reference unitsindicative of a distance between each of the respective reference unitsand an object in the coverage areas associated with the respectivereference unit. These corresponding signals received from the referenceunits can be processed to determine a location of the object.

A further embodiment disclosed herein includes a method of tracking anobject using at least one fiber optic reference array cable as disclosedherein. In one embodiment, the method comprises transmitting a RF signalfrom at least one antenna of a plurality of the multiple reference unitsto respective coverage areas associated with the respective referenceunits. The coverage areas may be picocellular coverage areas as anexample. The RF signal may be an UWB RF signal, as an example.Corresponding signals are received at a plurality of the multiplereference units from an object in the corresponding picocellularcoverage area. A distance from each of a plurality of the respectivereference units to the object is determined to obtain a plurality ofdetermined distances based on the received corresponding signal. Thelocation of the object is determined based on the plurality ofdetermined distances.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theinvention as described herein, including the detailed description thatfollows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments, and are intendedto provide an overview or framework for understanding the nature andcharacter of the disclosure. The accompanying drawings are included toprovide a further understanding, and are incorporated into andconstitute a part of this specification. The drawings illustrate variousembodiments, and together with the description serve to explain theprinciples and operation of the concepts disclosed.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other features, aspects, and advantages of the presentdisclosure may be better understood when the following detaileddescription is read with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic diagram of an exemplary generalized embodiment ofan optical-fiber-based wireless picocellular system;

FIG. 2 is a more detailed schematic diagram of an exemplary embodimentof the system of FIG. 1;

FIG. 3A is a close-up schematic diagram of an exemplary fiber opticarray cable according to one embodiment;

FIG. 3B is a schematic diagram similar to FIG. 3A, illustrating analternate embodiment of a fiber optic array cable;

FIG. 4 is a schematic diagram of an exemplary embodiment of anoptical-fiber-based wireless picocellular system that includes a centralhead-end station.

FIG. 5 is a detailed schematic diagram of an exemplary embodiment of acentral head-end station;

FIG. 6 is a view of one example of a reference unit located in a fiberoptic array cable, illustrating a corresponding picocell and theexchange of downlink and uplink electromagnetic signals between thereference unit and objects within the picocell;

FIG. 7 is a schematic diagram of an exemplary embodiment of acentralized optical-fiber-based wireless picocellular system thatincludes multiple optical fiber cables optically coupled to the centralhead-end station;

FIG. 8 is a “top down” view of the system of FIG. 7, showing anexemplary extended picocellular coverage area formed by using multipleoptical fiber cables;

FIG. 9 is a schematic cut-away diagram of an exemplary buildinginfrastructure in which an exemplary optical-fiber-based wirelesspicocellular system might be used;

FIG. 10 is a schematic “top down” view of one floor of the buildinginfrastructure of FIG. 9, showing multiple fiber optic array cablesextending over the ceiling of the floor of the building;

FIG. 11 is a schematic view of an exemplary deployment of four fiberoptic reference array cables on top of ceiling tiles to providethree-dimensional location tracking;

FIG. 12 illustrates a two-dimensional location tracking system usingthree reference nodes;

FIG. 13 illustrates how a two-dimensional location tracking system usingthree reference nodes fails when three lines of sight are not available;

FIG. 14 is a flow chart showing the steps of an exemplary method oftracking the location of objects using an exemplary fiber opticreference array cable system;

FIG. 15 is a schematic view of an exemplary deployment of a fiber opticarray cable system in a train;

FIG. 16 is a schematic view of an exemplary deployment of a fiber opticarray cable system in an indoor setting to determine the optimal WLANaccess point for a user;

FIG. 17 is a schematic view of an exemplary deployment of a fiber opticarray cable system in an indoor setting to help assist in placing andlocating emergency 911 calls;

FIG. 18A is a schematic diagram of an exemplary reference unit locatedin a fiber optic array cable system showing two separate antennas;

FIG. 18B is a schematic diagram of an exemplary reference unit locatedin a fiber optic array cable system showing one antenna and a RF switch;

FIG. 19A is a schematic diagram of an exemplary remote head-end unitcorresponding to the optical switching of signals between a fiber opticarray cable and a fiber optic pair;

FIG. 19B is a schematic diagram of an exemplary remote head-end unitcorresponding to the radio frequency switching between an electricalcable array and one bi-directional electrical cable;

FIG. 20 is a schematic diagram showing the details of an exemplaryhead-end unit that enables the use of different sections of a singlefiber optic array cable for three-dimensional tracking of objects; and

FIG. 21 is a schematic diagram showing the details of an exemplaryhead-end unit that enables multiple services to be supported by a singlefiber optic array cable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, in which some, but not all embodiments are shown. Indeed, theconcepts may be embodied in many different forms and should not beconstrued as limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will satisfy applicablelegal requirements. Whenever possible, like reference numbers will beused to refer to like components or parts.

Embodiments disclosed in the detailed description include fiber opticarray cables and related systems and methods. Such cables, systems, andmethods can be employed to determine and/or track the location of anobject. The fiber optic array cable can be employed in anoptical-fiber-based communication system, including but not limited to acentralized optical-fiber-based communication system. In one embodiment,the fiber optic array cable includes multiple reference units along thelength of the cable. Each reference unit in the fiber optic array cablecan include an antenna, and an electrical-to-optical (E/O) converter andan optical-to-electrical (O/E) converter to convert electrical RFsignals to optical RF signals, and vice versa, respectively. Thereference units can be configured to convert received optical RF signalsinto electrical RF signals to establish RF communications with objectscapable of receiving electrical RF signals. The reference units can alsobe configured to convert received electrical RF signals from the objectsinto optical RF signals, which are then used to determine the locationof the object.

Having the availability of the multiple reference units on one or moreof the fiber optic array cables can provide enhanced reliability intracking objects, including objects in an indoor environment. Themultiple reference units of the fiber optic array cables disclosedherein can increase the probability of having sufficient communicationpaths to the object being tracked. Further, providing the multiplereference units in a fiber optic array cable allows the use of opticalfiber as a transmission medium for communications to the trackedobjects. The fiber optic array cables may be provided such that remoteobjects can be tracked using high bandwidth optical fiber.

According to one embodiment disclosed herein, RF signals, such asUltraWideBand-Impulse Radio (UWB-IR) signals for example, can betransmitted over the fiber optic array cables to determine and/or trackthe location of the object. Systems using UWB-IR signals in particular,although not limiting herein, can provide accurate ranging capability.The accurate ranging capability of UWB-IR systems does not deterioratewhen UWB-IR signals are transmitted over a centralized RoF system. Thus,by transmitting UWB-IR signals over a centralized optical-fiber-basedcommunication system that includes one or more fiber optic array cableshaving multiple reference units, accurate and reliable three-dimensionaltracking of a target object can be enabled.

Before discussing the particular systems and methods for locationtracking of an object by transmitting RF signals, including UWB-IRsignals in one embodiment, over a centralized RoF communication systemthat includes one or more of the fiber optic reference array cableshaving multiple reference units, FIGS. 1-10 are provided to discussexamples of an optical-fiber-based wireless communication system whichmay employ the fiber optic array cables and other systems and methodsdescribed herein to track the location of an object.

FIG. 1 is a schematic diagram of a generalized embodiment of anoptical-fiber-based wireless picocellular system 10. The system 10includes a head-end unit 20, one or more transponder or remote antennaunits 30, or simply “remote units” 30, and an optical fiber RFcommunication link 36 that optically couples the head-end unit 20 to theremote unit 30. As discussed in detail below, system 10 has a picocell40 substantially centered about remote unit 30. The remote units 30 forma picocellular coverage area 44. When the remote units 30 are used in afiber optic reference array cable for the purpose of tracking thelocation of an object, as discussed below, the remote units 30 arehereafter referred to as “reference units 30.” The head-end unit 20 isadapted to perform or to facilitate any one of a number of RF-over-fiberapplications, such as radio-frequency identification (RFID), wirelesslocal area network (WLAN) communication, or cellular phone service.Shown within the picocell 40 is a device 45. The device 45 may be anobject to be tracked which includes a tag 46 adapted to receive and/orsend electromagnetic RF signals.

FIG. 2 is a schematic diagram of an exemplary embodiment of the system10 of FIG. 1. In this exemplary embodiment, the head-end unit 20includes a service unit 50 that provides electrical RF service signalsfor a particular wireless service or application. The service unit 50provides electrical RF service signals by passing (or conditioning andthen passing) such signals from one or more outside networks 223, asdescribed below. In a particular embodiment, this may include providingUWB-IR signal distribution in the range of 3.1 to 10.6 GHz. Other signaldistribution is also possible, including WLAN signal distribution asspecified in the IEEE 802.11 standard, i.e., in the frequency range from2.4 to 2.5 GHz and from 5.0 to 6.0 GHz. In another embodiment, theservice unit 50 may provide electrical RF service signals by generatingthe signals directly.

The service unit 50 is electrically coupled to an E/O converter 60 thatreceives an electrical RF service signal from the service unit 50 andconverts it to corresponding optical signal, as discussed in furtherdetail below. In an exemplary embodiment, the E/O converter 60 includesa laser suitable for delivering sufficient dynamic range for theRF-over-fiber applications, and optionally includes a laserdriver/amplifier electrically coupled to the laser. Examples of suitablelasers for the E/O converter 60 include laser diodes, distributedfeedback (DFB) lasers, Fabry-Perot (FP) lasers, and vertical cavitysurface emitting lasers (VCSELs).

The head-end unit 20 also includes an O/E converter 62 electricallycoupled to the service unit 50. The O/E converter 62 receives an opticalRF service signal and converts it to a corresponding electrical signal.In one embodiment, the O/E converter is a photodetector, or aphotodetector electrically coupled to a linear amplifier. The E/Oconverter 60 and the O/E converter 62 constitute a “converter pair” 66.

In an exemplary embodiment, the service unit 50 includes a RF signalmodulator/demodulator unit 70 that generates an RF carrier of a givenfrequency and then modulates RF signals onto the carrier. Themodulator/demodulator unit 70 also demodulates received RF signals. Theservice unit 50 also includes a digital signal processing unit (“digitalsignal processor”) 72, a central processing unit (CPU) 74 for processingdata and otherwise performing logic and computing operations, and amemory unit 76 for storing data, such as system settings, statusinformation, RFID tag information, etc. In an exemplary embodiment, thedifferent frequencies associated with the different signal channels arecreated by the modulator/demodulator unit 70 generating different RFcarrier frequencies based on instructions from the CPU 74. Also, asdescribed below, the common frequencies associated with a particularcombined picocell are created by the modulator/demodulator unit 70generating the same RF carrier frequency.

With continuing reference to FIG. 2, in one embodiment, a reference unit30 includes a converter pair 66, wherein the E/O converter 60 and theO/E converter 62 therein are electrically coupled to an antenna system100 via a RF signal-directing element 106, such as a circulator. The RFsignal-directing element 106 serves to direct the downlink and uplinkelectrical RF service signals, as discussed below. In an exemplaryembodiment, the antenna system 100 includes a broadband (3.1 to 10.6GHz) antenna integrated into a specialized fiber-optic array cable, asshown and discussed below with reference to FIGS. 3A and 3B.

The reference units 30 differ from the typical access point deviceassociated with wireless communication systems in that the preferredembodiment of the reference unit 30 has just a few signal-conditioningelements and no digital information processing capability. Rather, theinformation processing capability is located remotely in head-end unit20, and in a particular example, in service unit 50. This allowsreference unit 30 to be very compact and virtually maintenance free. Inaddition, the preferred exemplary embodiment of the reference unit 30consumes very little power, is transparent to RF signals, and does notrequire a local power source, as described below.

With reference again to FIG. 2, an exemplary embodiment of the opticalfiber RF communication link 36 includes a downlink optical fiber 136Dhaving an input end 138 and an output end 140, and an uplink opticalfiber 136U having an input end 142 and an output end 144. The downlinkand uplink optical fibers 136D and 136U optically couple converter pair66 at head-end unit 20 to the converter pair 66 at reference unit 30.Specifically, the downlink optical fiber input end 138 is opticallycoupled to the E/O converter 60 of the head-end unit 20, while theoutput end 140 is optically coupled to the O/E converter 62 at thereference unit 30. Similarly, the uplink optical fiber input end 142 isoptically coupled to E/O converter 60 of the reference unit 30, whilethe output end 144 is optically coupled to the O/E converter 62 at thehead-end unit 20.

In one embodiment, the system 10 employs a known telecommunicationswavelength, such as 850 nm, 1300 nm, or 1550 nm. In another exemplaryembodiment, the system 10 employs other less common but suitablewavelengths such as 980 nm.

Exemplary embodiments of the system 10 include either single-modeoptical fiber or multimode optical fiber for downlink and the uplinkoptical fibers 136D and 136U. The particular type of optical fiberdepends on the application of the system 10. For many in-buildingdeployment applications, maximum transmission distances typically do notexceed 300 meters. The maximum length for the intended RF-over-fibertransmission needs to be taken into account when considering usingmulti-mode optical fibers for the downlink and uplink optical fibers136D and 136U. For example, it has been shown that a 1400 MHz/kmmulti-mode fiber bandwidth-distance product is sufficient for 5.2 GHztransmission up to 300 m.

In one embodiment, a 50 μm multi-mode optical fiber is used for thedownlink and uplink optical fibers 136D and 136U, and the E/O converters60 operate at 850 nm using commercially available VCSELs specified for10 Gb/s data transmission. In a more specific exemplary embodiment, OM350 μm multi-mode optical fiber is used for the downlink and uplinkoptical fibers 136D and 136U.

System 10 also includes a power supply 160 that generates an electricalpower signal 162. The power supply 160 is electrically coupled to thehead-end unit 20 for powering the power-consuming elements therein. Inone embodiment, an electrical power line 168 runs through the head-endunit 20 and over to the reference unit 30 to power the E/O converter 60and the O/E converter 62 in the converter pair 66, the optional RFsignal-directing element 106 (unless element 106 is a passive devicesuch as a circulator), and any other power-consuming elements (notshown). In an exemplary embodiment, the electrical power line 168includes two wires 170 and 172 that carry a single voltage and that areelectrically coupled to a DC power converter 180 at the reference unit30. DC power converter 180 is electrically coupled to the E/O converter60 and the O/E converter 62, and changes the voltage or levels of theelectrical power signal 162 to the power level(s) required by thepower-consuming components in the reference unit 30. In one embodiment,the DC power converter 180 is either a DC/DC power converter, or anAC/DC power converter, depending on the type of electrical power signal162 carried by the electrical power line 168. In an exemplaryembodiment, the electrical power line 168 includes standardelectrical-power-carrying electrical wire(s), e.g., 18-26 AWG (AmericanWire Gauge) used in standard telecommunications and other applications.In another exemplary embodiment, the electrical power line 168 (dashedline) runs directly from the power supply 160 to the reference unit 30rather than from or through the head-end unit 20. In another exemplaryembodiment, the electrical power line 168 includes more than two wiresand carries multiple voltages.

In another embodiment, the head-end unit 20 is operably coupled to anoutside network 223 via a network link 224.

With reference to the optical-fiber-based wireless picocellular system10 of FIG. 1 and FIG. 2, the service unit 50 generates an electricaldownlink RF service signal SD (“electrical signal SD”) corresponding toits particular application. In one embodiment, this is accomplished bythe digital signal processor 72 providing the modulator/demodulator unit70 with an electrical signal (not shown) that is modulated onto a RFcarrier to generate a desired electrical signal SD. The electricalsignal SD is received by the E/O converter 60, which converts thiselectrical signal SD into a corresponding optical downlink RF signal SD′(“optical signal SD′”), which is then coupled into downlink opticalfiber 136D at the input end 138. It is noted here that in one embodimentthe optical signal SD′ is tailored to have a given modulation index.Further, in an exemplary embodiment the modulation power of the E/Oconverter 60 is controlled (e.g., by one or more gain-controlamplifiers, not shown) to vary the transmission power from the antennasystem 100. In an exemplary embodiment, the amount of power provided tothe antenna system 100 is varied to define the size of the associatedpicocell 40, which in exemplary embodiments range anywhere from about ameter across to about twenty meters across.

The optical signal SD′ travels over the downlink optical fiber 136D tothe output end 140, where it is received by the O/E converter 62 inreference unit 30. The O/E converter 62 converts the optical signal SD′back into electrical signal SD, which then travels to thesignal-directing element 106. The signal-directing element 106 thendirects the electrical signal SD to the antenna system 100. Theelectrical signal SD is fed to the antenna system 100, causing it toradiate a corresponding electromagnetic downlink RF signal SD″(“electromagnetic signal SD″”).

When the device 45 is an object to be tracked and is located within thepicocell 40, the electromagnetic signal SD″ is received by the tag 46.The tag 46 may be a RFID tag, a sensor, or part of a wireless card, or acell phone antenna, for example. The tag 46 converts the electromagneticsignal SD″ into an electrical signal SD in the device 45, and processesthe electrical signal SD. The tag 46 can generate electrical uplink RFsignals SU, which are converted into electromagnetic uplink RF signalsSU″ (“electromagnetic signal SU″”) by an antenna associated with tag 46.

When the device 45 is an object to be tracked and is located within thepicocell 40, the electromagnetic signal SU″ is detected by the antennasystem 100 in the reference unit 30, which converts this signal backinto an electrical signal SU. The electrical signal SU is directed bythe signal-directing element 106 to the E/O converter 60, which convertsthis electrical signal into a corresponding optical uplink RF signal SU′(“optical signal SU′”), which is then coupled into the input end 142 ofthe uplink optical fiber 136U. The optical signal SU′ travels over theuplink optical fiber 136U to the output end 144, where it is received bythe O/E converter 62 at the head-end unit 20. The O/E converter 62converts the optical signal SU′ back into electrical signal SU, which isthen directed to the service unit 50. The service unit 50 receives andprocesses electrical signal SU, which in one embodiment includes one ormore of the following: storing the signal information; digitallyprocessing or conditioning the signals; sending the signals on to one ormore outside networks 223 via network links 224; and sending the signalsto one or more devices 45 in the picocellular coverage area 44. In anexemplary embodiment, the processing of electrical signal SU includesdemodulating the electrical signal SU in the modulator/demodulator unit70, and then processing the demodulated signal in the digital signalprocessor 72.

FIG. 3A is a close-up schematic diagram of an exemplary fiber opticarray cable 336 that may be used in conjunction with theoptical-fiber-based wireless picocellular system 10. Fiber optic arraycable 336 includes a downlink optical fiber 336D and an uplink opticalfiber 336U that extend along the length of the fiber optic array cable336. At various points along the fiber optic array cable 336 arereference units 30. Two reference units 30 are shown, but any number maybe used. The reference units 30 may be evenly spaced along the fiberoptic array cable 336, but they need not be. In a preferred embodiment,the reference units 30 are placed 4 meters apart. The reference units 30include E/O and O/E conversion capability, which may be implemented by aconverter pair like converter pair 66 in FIG. 2. Each reference unit 30has at least one broadband antenna 300. The broadband antenna 300 isadapted to send and receive UWB signals in the range of 3.1 to 10.6 GHz.Also shown is the electrical power line 168 electrically coupled to thereference units 30.

In an exemplary embodiment, the fiber optic array cable 336 includes aprotective outer jacket 344. In an exemplary embodiment, the referenceunits 30 reside completely within the outer jacket 344. FIG. 3B is aschematic diagram similar to FIG. 3A, illustrating an exemplaryembodiment wherein the reference units 30 lie outside of protectiveouter jacket 344. Locating the reference units 30 outside of theprotective outer jacket 344 may make it easier to arrange the referenceunits relative to a building infrastructure after the optical fibercable is deployed, as described below.

Alternately, the reference units 30 may be provided in a tether cable(not shown) that is connected to the fiber optic array cable 336.

FIG. 4 is a schematic diagram of an exemplary embodiment of anoptical-fiber-based wireless picocellular system 200 that includes acentral head-end station 210. The central head-end station 210 can bethought of as a head-end unit 20 adapted to handle one or more serviceunits 50 and one or more reference units 30. Central head-end station210 is optically coupled to an optical fiber cable 220 that includesmultiple reference units 30. The optical fiber cable 220 is constitutedby multiple optical fiber RF communication links 36 (FIG. 2), with eachlink optically coupled to a corresponding reference unit 30. In oneembodiment, multiple reference units 30 are spaced apart along thelength of the optical fiber cable 220 (e.g., at 4 or 8 meter intervalsin exemplary embodiments) to create a desired picocellular coverage area44 comprised of picocells 40, which may overlap at their edges.

FIG. 5 is a detailed schematic diagram of an exemplary embodiment of thecentral head-end station 210. Rather than including multiple head-endunits 20 of FIG. 1 directly into central head-end station 210, in anexemplary embodiment the head-end units 20 are modified to allow foreach service unit 50 to communicate with one, some, or all of thereference units 30, depending on the particular application of a givenservice unit 50. The service units 50 are each electrically coupled to aRF transmission line 230 and a RF receiving line 232. In FIG. 5, onlythree of six service units 50A through 50F are shown for the purposes ofclarifying the illustration.

In one embodiment, the system 200 further includes a main controller 250operably coupled to the service units 50 and adapted to control andcoordinate the operation of the service units 50 in communicating withthe reference units 30. In an exemplary embodiment, the main controller250 includes a CPU 252 and a memory unit 254 for storing data. The CPU252 is adapted (e.g., is programmed) to process information provided tothe main controller 250 by one or more of service units 50. In anexemplary embodiment, the main controller 250 is or includes aprogrammable computer adapted to carry out instructions (programs)provided to it or otherwise encoded therein on a computer-readablemedium.

The central head-end station 210 further includes a downlink RF signalmultiplexer (“downlink multiplexer”) 270 operably coupled to the maincontroller 250. The downlink multiplexer 270 has an input side 272 andan output side 274. RF transmission lines 230 are electrically connectedto the downlink multiplexer 270 at the input side 272.

In an exemplary embodiment, the downlink multiplexer 270 includes a RFsignal-directing element 280 (e.g., a RF switch) that allows forselective communication between the service units 50 and the referenceunits 30, as described below. In an example, the selective communicationinvolves sequentially addressing reference units 30 for pollingcorresponding picocells 40. Such sequential polling may be used, forexample, when one of the service units 50 is a RFID reader searching forRFID tags 46 in picocells 40 (FIG. 4). In an exemplary embodiment, thetags 46 are attached to device 45 if device 45 is an item to be trackedor otherwise monitored via the attached tag 46. In another exemplaryembodiment, the selective communication involves simultaneouslyaddressing some or all of the reference units 30. Such simultaneousaddressing can be used, for example, when one of the service units 50 isa cellular phone transmitter or a RF-signal feed-through unit thatprovides simultaneous coverage of some or all of the picocells 40.

The central head-end station 210 also includes an uplink RF signalmultiplexer (“uplink multiplexer”) 320 operably coupled to the maincontroller 250 and having an input side 322 and an output side 324.Receiving lines 232 are electrically connected to the uplink multiplexer320 at the output side 324. In an exemplary embodiment, the uplinkmultiplexer 320 includes a RF signal-directing element 328.

The central head-end station 210 also includes a number of E/Oconverters 60 that make up an E/O converter array 360, and acorresponding number of O/E converters 62 that make up an O/E converterarray 362. The E/O converters 60 are electrically coupled to the outputside 274 of downlink multiplexer 270 via electrical lines 332, and areoptically coupled to the input ends 138 of corresponding downlinkoptical fibers 136D. The O/E converters 62 are electrically coupled tothe input side 322 of the uplink multiplexer 320 via the electricallines 334, and are optically coupled to the output ends 144 of thecorresponding uplink optical fiber 136U. The downlink optical fibers136D constitute a downlink optical fiber cable 378 and the uplinkoptical fibers 136U constitute an uplink optical fiber cable 380.

With reference to FIGS. 3A, 3B, 4, and 5, the optical-fiber-basedwireless picocellular system 200 operates as follows. At the centralhead-end station 210, the service units 50A, 50B, . . . 50F eachgenerate or pass through from one or more outside networks 223respective electrical signals SD that correspond to the particularapplication of the given service unit. The electrical signals SD aretransmitted over the RF transmission lines 230 to the downlinkmultiplexer 270. The downlink multiplexer 270 then combines (infrequency) and distributes the various electrical signals SD to the E/Oconverters 60 in the E/O converter array 360. In an exemplaryembodiment, the downlink multiplexer 270 and RF signal-directing element280 therein are controlled by the main controller 250 via a controlsignal S1 to the direct electrical signals SD to one, some, or all ofthe E/O converters 60 in the E/O converter array 360 and thus to one,some or all of the reference units 30, based on the particular serviceunit application. For example, if service unit 50A is a cellular phoneunit, then in an exemplary embodiment the electrical signals SDtherefrom (e.g., passing therethrough from one or more outside networks223) are divided (and optionally amplified) equally by the RFsignal-directing element 280 and provided to each E/O converter 60 inE/O converter array 360. This results in each reference unit 30 beingaddressed. On the other hand, if the service unit 50F is a WLAN serviceunit, then RF signal-directing element 280 may be adapted (e.g.,programmed) to direct electrical signals SD to select ones of the E/Oconverters 60 in E/O converter array 360 so that only select referenceunits 30 are addressed.

Thus, one, some, or all of the E/O converters 60 in the E/O converterarray 360 receive the electrical signals SD from the downlinkmultiplexer 270. The addressed E/O converters 60 in the E/O converterarray 360 convert the electrical signals SD into corresponding opticalsignals SD′, which are transmitted over the corresponding downlinkoptical fibers 136D to the corresponding reference units 30. Theaddressed reference units 30 convert the optical signals SD′ back intoelectrical signals SD, which are then converted into electromagneticsignals SD″ that correspond to the particular service unit application.

FIG. 6 is a close-up view of one of the reference units 30, illustratingthe corresponding picocell 40 and the exchange of downlink and uplinkelectromagnetic signals SD″ and SU″ between the reference units 30 andthe devices 45 within the picocell 40. In particular, theelectromagnetic signals SU″ are received by the corresponding referenceunit 30 and converted to electrical signals SU, and then to opticalsignals SU′. The optical signals SU′ then travel over the uplink opticalfiber 136U and are received by the O/E converter array 362 and thecorresponding O/E converters 62 therein for the addressed referenceunits 30. The O/E converters 62 convert the optical signals SU′ back toelectrical signals SU, which then proceed to the uplink multiplexer 320.The uplink multiplexer 320 then distributes the electrical signals SU tothe service unit(s) 50 that require(s) receiving these electricalsignals SU. The receiving service units 50 process the electricalsignals SU, which in an exemplary embodiment includes one or more of:storing the signal information; digitally processing or conditioning thesignals; sending the signals on to one or more outside networks 223 viathe network links 224; and sending the signals to one or more devices 45in the picocellular coverage area 44.

In an exemplary embodiment, the uplink multiplexer 320 and the RFsignal-directing element 328 therein are controlled by the maincontroller 250 via a control signal S2 (see FIG. 5) to direct electricalsignals SU to the service unit(s) 50 that require(s) receivingelectrical signals SU. Different services from some or all of theservice units 50 (i.e., cellular service, WiFi for data communication,RFID monitoring, etc.) may be combined at the RF signal level byfrequency multiplexing.

In an exemplary embodiment, a single electrical power line 168 from thepower supply 160 at central head-end station 210 is incorporated intothe optical fiber cable 220 and is adapted to power each reference unit30, as shown in FIGS. 3A and 3B. Each reference unit 30 taps off theneeded amount of power, e.g., via a DC power converter 180 (FIG. 2).Since the preferred embodiment of a reference unit 30 has relatively lowfunctionality and power consumption, only relatively low electricalpower levels are required (e.g., ˜1 watt), allowing high-gauge wires tobe used (e.g., 20 AWG or higher) for the electrical power line 168. Inan exemplary embodiment that uses many reference units 30 (e.g., morethan twelve) in the optical fiber cable 220, or if the power consumptionfor the reference units 30 is significantly larger than 1 watt due totheir particular design, lower-gauge wires or multiple wires areemployed in the electrical power line 168. The inevitable voltage dropalong the electrical power line 168 within the optical fiber cable 220typically requires large-range (˜30 volts) voltage regulation at eachreference unit 30. In an exemplary embodiment, DC power converters 180at each reference unit 30 perform this voltage regulation function. Ifthe expected voltage drop is known, then in an exemplary embodiment themain controller 250 carries out the voltage regulation. In analternative embodiment, remote voltage sensing at each reference unit 30is used, but this approach is not the preferred one because it addscomplexity to the system.

FIG. 7 is a schematic diagram of an exemplary embodiment of acentralized optical-fiber-based wireless picocellular system 400. Thesystem 400 is similar to the system 200 as described above, but includesmultiple optical fiber cables 220 optically coupled to the centralhead-end station 210. The central head-end station 210 includes a numberof E/O converter arrays 360 and a corresponding number of O/E converterarrays 362, arranged in pairs in converter array units 410, with oneconverter array unit 410 optically coupled to one optical fiber cable220. Likewise, the system 400 includes a number of downlink multiplexers270 and uplink multiplexers 320, arranged in pairs in multiplexer units414, with one multiplexer unit 414 electrically coupled to one converterarray unit 410. In an exemplary embodiment, the main controller 250 iselectrically coupled to each multiplexer unit 414 and is adapted tocontrol the operation of the downlink and uplink multiplexers 270 and320 therein. Here, the term “array” is not intended to be limited tocomponents integrated onto a single chip as is often done in the art,but includes an arrangement of discrete, non-integrated components.

Each E/O converter array 360 is electrically coupled to the downlinkmultiplexer 270 in the corresponding multiplexer unit 414. Likewise,each O/E converter array 362 is electrically coupled to the uplinkmultiplexer 320 in the corresponding multiplexer unit 414. The serviceunits 50 are each electrically coupled to both downlink and uplinkmultiplexers 270 and 320 within each multiplexer unit 414. Respectivedownlink and uplink optical fiber cables 378 and 380 optically coupleeach converter array unit 410 to a corresponding optical fiber cable220. In an exemplary embodiment, the central head-end station 210includes connector ports 420 and optical fiber cables 220 includeconnectors 422 adapted to connect to the connector ports 420. In anexemplary embodiment, the connectors 422 are MT (“Mechanical Transfer”)connectors, such as the UNICAM® MTP connector available from CorningCable Systems, Inc., Hickory, N.C. In an exemplary embodiment, theconnectors 422 are adapted to accommodate the electrical power line 168connected to the connector ports 420.

FIG. 8 is a “top down” view of the system 400, showing an extendedpicocellular coverage area 44 formed by using multiple optical fibercables 220. In an exemplary embodiment, the system 400 supports anywherefrom two reference units 30, to hundreds of reference units 30, to eventhousands of reference units 30. The particular number of referenceunits 30 employed is not fundamentally limited by the design of thesystem 400, but rather by the particular application.

In FIG. 8, the picocells 40 are shown as non-overlapping. Thisnon-overlap is based on adjacent reference units 30 operating atslightly different frequencies to avoid the otherwise undesirablesubstantial overlap that occurs between adjacent picocells 40 thatoperate at the same frequency.

System 400 operates in a manner similar to the system 200 as describedabove, except that instead of reference units 30 being in a singleoptical fiber cable 220, the reference units 30 are distributed over twoor more optical fiber cables 220 through the use of corresponding two ormore converter array units 410. Electrical signals SD from the serviceunits 50 are distributed to each multiplexer unit 414. The downlinkmultiplexers 270 therein convey electrical signals SD to one, some, orall of the converter array units 410, depending on which reference units30 are to be addressed by which service unit 50. Electrical signals SDare then processed as described above, with downlink optical signals SD′being sent to one, some, or all of reference units 30. Uplink opticalsignals SU′ generated by devices in the corresponding picocells 40return to the corresponding converter array units 410 at the centralhead-end station 210. The optical signals SU′ are converted toelectrical signals SU at the receiving converter array unit(s) 410 andare then sent to the uplink multiplexers 320 in the correspondingmultiplexer unit(s) 414. The uplink multiplexers 320 therein are adapted(e.g., programmed by main controller 250) to direct electrical signalsSU to the service unit(s) 50 that require(s) receiving electricalsignals SU. The receiving service units 50 process the electricalsignals SU, which as discussed above in an exemplary embodiment includesone or more of: storing the signal information; digitally processing orconditioning the signals; sending the signals on to one or more outsidenetworks 223 via network links 224; and sending the signals to one ormore client devices 45 in the picocellular coverage area 44.

FIG. 9 is a schematic cut-away diagram of a building infrastructure 500that generally represents any type of building in which theoptical-fiber-based wireless picocellular system would be useful, suchas office buildings, schools, hospitals, college buildings, airports,warehouses, etc. The building infrastructure 500 includes a first(ground) floor 501, a second floor 502, and a third floor 503. The firstfloor 501 is defined by a floor 510 and a ceiling 512; the second floor502 is defined by a floor 520 and a ceiling 522; and the third floor 503is defined by a floor 530 and a ceiling 532. An exemplary centralizedoptical-fiber-based wireless picocellular system, such as system 400, isincorporated into building infrastructure 500 to provide a picocellularcoverage area 44 that covers floors 501, 502, and 503.

An exemplary embodiment involves tailoring or designing the picocellularcoverage areas 44 for the different floors 501, 502, and 503 to suitparticular needs. FIG. 10 is a schematic “top down” view of the secondfloor 502 of the building infrastructure 500, showing three opticalfiber cables 220 branching out from the MC connector 550 and extendingover the ceiling 522. The picocells 40 associated with reference units30 (not shown in FIG. 10) form an extended picocellular coverage area 44that covers the second floor 502 with fewer, larger picocells than thefirst and third floors 501 and 503 (FIG. 9). Such different picocellularcoverage areas 44 may be desirable when the different floors havedifferent wireless needs. For example, the third floor 503 might requirerelatively dense picocell coverage if it serves as storage for itemsthat need to be inventoried and tracked via RFID tags 46. Likewise, thesecond floor 502 may be office space that calls for larger and fewerpicocells to provide cellular phone service and WLAN coverage.

One application of picocellular wireless systems, including theoptical-fiber-based wireless picocellular system 200, as shown in FIGS.4 and 5, or the optical-fiber-based wireless picocellular system 400, asshown in FIGS. 7 and 8, that may comprise a fiber optical array cable336 as shown in FIGS. 3A and 3B, involves providing a number ofdifferent services (e.g., WLAN, voice, RFID tracking, temperature,and/or light control) within a building, usually by deploying one ormore optical fiber cables close to the ceiling. For example,ultrawideband (UWB) radios can have relative bandwidths larger thantwenty percent (20%) or absolute bandwidths of more than 500 MHz, whichoffer advantages for communication applications. In particular, UWB-IRtechnology offers the advantage of providing accurate ranginginformation, which results from the inherent narrow time signature ofbroadband pulses. Thus, while not limiting, UWB-IR technology may beused for target sensor data collection, precision locating, and trackingof objects. UWB refers to signals which spread across many frequencybands that are allocated to different purposes. Thus, its use involvesco-existence and electromagnetic compatibility (EMC) considerations. Asper Federal Communications Commission (FCC) regulations, the EffectiveIsotropic Radiated Power (EIRP) of these devices is restricted to lessthan −41.3 dBm/MHz. The low EIRP makes UWB technology attractive inenvironments (e.g., hospitals) where electromagnetic interference couldcause device malfunctions. However, this EIRP restriction also imposessignificant limitations on the range of operation of these signals whencompared to traditional 802.11 Wireless Local Area Network (WLAN)technology. Another issue with UWB-IR is that it requires multiple Lineof Sight (LoS) signals to provide accurate range information.

According to one embodiment disclosed herein, UWB-IR signals aretransmitted over a centralized RoF system of the type discussed abovethat includes one or more of the fiber optic reference array cablesdisclosed herein. The accurate ranging capability of UWB-IR systems doesnot deteriorate when UWB-IR signals are transmitted over a centralizedRoF system. Thus, by transmitting UWB-IR signals over a centralized RoFsystem that includes a fiber optic reference array cable with multiplereference units, accurate and reliable three dimensional tracking of atarget object in environments, including indoor environments, can beenabled.

FIG. 11 is a schematic view of an exemplary deployment of four fiberoptic array cables 336 on top of ceiling tiles to providethree-dimensional location tracking, according to one embodiment. Eachfiber optic array cable 336 has multiple reference units 30 that includeat least one E/O and O/E converter pair 66 and at least one antenna 100.In a preferred embodiment, the antenna 100 is an UWB-IR antenna adaptedto send and receive UWB signals in the range of 3.1 to 10.6 GHz. Thenumber of fiber optic array cables 336 and the pattern in which thefiber optic array cables 336 are arranged is not critical. However, itis beneficial if there are enough reference units 30 in the fiber opticarray cables 336 to avoid blocking-induced loss of tracking.

FIG. 12 illustrates a prior art two-dimensional location tracking systemusing three reference nodes. FIG. 12 shows two dimensional tracking withthe help of three reference nodes. The location of the object can beobtained by using a time of arrival based algorithm, which includessolving the following equation for (x_(i), y_(i)).

${{2\begin{bmatrix}( {{x\; 3} - {x\; 1}} ) & ( {{y\; 3} - {y\; 1}} ) \\( {{x\; 3} - {x\; 2}} ) & ( {{y\; 3} - {y\; 2}} )\end{bmatrix}}\begin{bmatrix}{xi} \\{yi}\end{bmatrix}} = \begin{bmatrix}{{D\; 1^{2}} - {D\; 3^{2}} - {x\; 1^{2}} - {y\; 1^{2}} + {x\; 3^{2}} + {y\; 3^{2}}} \\{{D\; 2^{2}} - {D\; 3^{2}} - {x\; 2^{2}} - {y\; 2^{2}} + {x\; 3^{2}} + {y\; 3^{2}}}\end{bmatrix}$

To perform the time of arrival based algorithm, one would need at leastthree reference nodes for doing tracking in two dimensions, and wouldneed four reference nodes in order to do tracking in three dimensions.Moreover, if one of the reference nodes is blocked, such as by a wall orother obstacle, the location finding algorithm becomes unstable.

FIG. 13 illustrates how a prior art two-dimensional location trackingsystem using three reference nodes fails when three lines of sight arenot available.

To avoid this problem, one or more fiber optic array cables 336 withmultiple reference units 30 are used to provide a reference array, asshown in FIG. 11. Having the availability of the extra reference units30 of the fiber optic array cables 336 of FIG. 11 provides enhancedreliability in tracking objects in an indoor environment. Theoptical-fiber-based wireless picocellular system includes a centralhead-end station 210 (see FIGS. 4, 5, 19A, 19B, 20, and 21) to providemanagement of the system to provide enhanced tracking by selecting oneor more reference units 30 from each fiber optic array cable 336 using aswitch, which in various exemplary embodiments may be a 1×N opticalswitch or a RF switch. In the event of a tracking algorithm failure dueto a blocking situation of the type shown in the prior art system ofFIG. 12, the switch could be activated to switch to another referenceunit combination in the fiber optic array cables 336 to mitigate theblocking-induced loss of tracking. The multiple reference units 30 ofthe fiber optic array cables 336 significantly increase the probabilityto have line of sight (LoS) paths to the object being tracked.

The installation of the fiber optic array cables 336 with multiplereference units 30, as shown in FIG. 11, also has the advantage of beingsimple. Four fiber optic array cables 336 can be laid on top of theceiling tiles, as shown in FIG. 11, in most buildings. It is alsopossible to lay a single fiber optic array cable 336 with at least fourreference units 30 that include an E/O and O/E converter pair 66 and anantenna 100, and then use optical switches in the central head-endstation 210, as shown in FIG. 20.

The availability of the multiple reference units 30 in the fiber opticarray cables 336 would also provide more than two equations to solve for(xi, yi), which results in more stable three-dimensional locationtracking. By using the accurate ranging UWB-IR signals over acentralized RoF wireless system that includes the fiber optic arraycables 336, a more efficient system of location tracking of objects isprovided.

FIG. 14 is a flow chart showing the steps of an exemplary method oftracking the location of objects using an exemplary fiber optic arraycable system, such as the one shown in FIG. 11.

The fiber optic array cables 336 are laid out as shown in FIG. 11 andlocations of the reference antennas 100 are assigned (block 1400). Thereference array may have n number of fiber optic array cables 336, witheach fiber optic array cable 336 having m number of reference units 30having an E/O and O/E converter pair 66 and an antenna 100 (with n and mboth being any number). One particular reference unit 30 is designatedas RA₁A₁ (block 1402) and that reference unit 30 is connected to thecentral head-end unit 210 (block 1404).

As discussed above with respect to FIGS. 3A, 3B, 4, and 5, a serviceunit 50 at the central head-end station 210 will generate or passthrough from one or more outside networks 223 an electrical signal SDthat corresponds to the particular application of the given service unit50. The electrical signal SD is then processed as discussed above todirect the electrical signal SD to the appropriate E/O converter 60 inthe E/O converter array 360 and thus as an optical signal SD′ to theselected reference unit 30 (RA₁A₁). This results in the selectedreference unit 30 being addressed. The addressed reference unit 30converts the optical signals SD′ back into electrical signals SD. Theelectrical signal SD is fed to an antenna 100, causing it to radiate acorresponding signal SD″. In one embodiment, the antenna 100 isconfigured to radiate a UWB signal. In an exemplary embodiment, the UWBsignal is transmitted at a frequency between 3.1 and 10.6 GHz.

When the device 45 is an object to be tracked that is located within thepicocell 40, a corresponding signal SD″ (which may be an UWB signal) isreceived by the tag 46. The tag 46 may be a RFID tag, or other sensor,such as part of a wireless card, or a cell phone antenna. The tag 46 cangenerate electromagnetic uplink RF signals SU″ (electromagnetic signalSU″”) in response to the received signal SD″ from the antenna 100. In anexemplary embodiment, the device 45 may have an antenna (not shown)associated with tag 46 that generates the electromagnetic uplink RFsignals SU″.

When the device 45 is an object to be tracked and is located within thepicocell 40, the electromagnetic signal SU″ is detected by the antennasystem 100 in the reference unit 30, which converts this signal backinto an electrical signal SU. The electrical signal SU is directed bythe signal-directing element 106 to the E/O converter 60, which convertsthis electrical signal into a corresponding optical signal SU′ (which isthen coupled into the input end 142 of the uplink optical fiber 136U.The optical signal SU′ travels over the uplink optical fiber 136U to theoutput end 144, where it is received by the O/E converter 62 at thehead-end unit 20. The O/E converter 62 converts the optical signal SU′back into electrical signal SU, which is then directed to the serviceunit 50. The service unit 50 receives and processes signal SU, which inthis case is used to measure the distance from the object to be tracked(OTT) to the reference unit 30.

At block 1406, the distance from RA₁A₁ to the OTT is measured using thetime of arrival algorithm as set forth above, or any known algorithm formeasuring distance. However, the algorithm must compensate for a time offlight delay introduced by the RoF system. This can be easily calibratedout by knowing the length of the fiber pairs connected to each referenceunit 30 on the fiber optic array cable 336.

At block 1408, the distance (D_(nm)) is then compared to a thresholddistance D_(nm) _(_) _(min/max) to ensure that the measured distance isaccurate. For example, the maximum threshold distance might be thedimensions of the room in which the fiber optic array cables 336 arelocated. If the measured distance is larger than the room dimensions,then the measured distance is deemed inaccurate and will not be used.One cause of an inaccurate measurement is that there is no LoS path fromthe selected reference unit 30 to the OTT due to a blocking obstacle.Another source of error may be cross talk with other signals. In thecase of any inaccurate measurement, another reference unit (m+1) in thefiber optic array cable 336 is selected (block 1410) and a check is madeat block 1412 (is m greater than the maximum number of reference units30 in the fiber optic array cable 336) to make sure the end of the fiberoptic array cable 336 has not been reached. The new reference unit(RA₁A₂) is connected to the central head-end station 210. Blocks 1406and 1408 are then repeated for the new reference unit.

If the measured distance (D_(nm)) is not greater than the maximumthreshold distance D_(nm) _(_) _(max), then the distance D_(nm) isrecorded at block 1414. A decision as to whether a reference unit 30 ineach of the four fiber optic array cables 336 has been selected (is n<4)is then performed at block 1416. Although the number of fiber opticarray cables 336 in FIG. 11 is four, the number may be less or more thanfour, although at least four is preferred to do three-dimensionaltracking of objects. If n is less than four in the example method ofFIG. 14, then a different fiber optic array cable 336 is selected(n=n+1) at block 1418 as long as a maximum number of fiber optic arrays336 has not been reached (block 1420). Blocks 1404 through 1414 are thenrepeated until four or more distances have been measured. Thethree-dimensional location of the OTT is then determined or calculatedusing a known trilateration algorithm. One can use a similar equation asdiscussed above, but with three variables (x, y, z), which requiresusing four measured distances from the OTT to the four reference units30 in the fiber optic array cable(s) 336. In one embodiment, onereference unit 30 from each of the four fiber optic array cables 336 canbe selected, and then the four measured distances can be used to solvefor the three-dimensional location of the object (xi, yi, zi). Adecision is then made at block 1424 as to whether tracking is to becontinued, and if so, then the process starts over at block 1402. Ifnot, the tracking process ends at block 1426.

Having the availability of the extra reference units 30 of the fiberoptic array cables 336 provides enhanced reliability in tracking objectsin an indoor environment by providing more LoS paths. The availabilityof the multiple reference units 30 in the fiber optic array cables 336would also provide more than two equations to solve for the location ofthe object, which results in more stable three-dimensional locationtracking.

In addition, since there may be multiple unused reference units 30 onthe fiber optic array cables 336, it is also possible to track multipleobjects at the same time using the same infrastructure.

Moreover, since the UWB-IR antennas are broadband and cover most of the802.11 bands, the reference units 30 on the fiber optic array cables 336can also be used for other wireless services in addition to trackingobjects.

For example, FIG. 15 is a schematic view of an exemplary deployment of afiber optic array cable 336 in a train where there is a WLAN accesspoint 1500. The fiber optic array cable 336 employing the UWB-IRantennas 100 at the reference units 30 can be used as discussed abovewith respect to FIG. 14 to determine the distance a user is from a knownWLAN access point 1500. Knowing the distance, the central head-endstation 210 can dynamically assign a stable WLAN access point 1500. Theassigned WLAN access point 1500 may be determined based on signalstrength, according to applicable WLAN standards, and/or the determinedor calculated distance. The WLAN can refuse to assign an access pointbased on the determined location, enabling data security. Real timeticket purchase with automatic seat recognition is also possible. Byhaving the multiple reference units 30 in the fiber optic array cables336, the distance can be determined or calculated even if there arepassengers or other objects blocking the signals from the UWB-IRantennas. Multiple fiber optic array cables 336 can be used to providemore UWB-IR antennas to provide more accurate positioning. In oneembodiment, the WLAN access point 1500 can also carry the UWB-IRsignals.

FIG. 16 is a schematic view of an exemplary deployment of a fiber opticarray cable 336 in an indoor setting to determine an optimal WLAN accesspoint for a user. In FIG. 16, one or more fiber optic array cables 336having multiple UWB-IR antennas 100 are deployed in the ceiling of abuilding or other location. There are also multiple WLAN access points1600 in the ceiling or located elsewhere in the building. The fiberoptic array cable 336 employing the UWB-IR antennas 100 at the referenceunits 30 can be used as discussed above with respect to FIG. 14 todetermine the distance a user is from a known WLAN access point 1600.Knowing the distance, the central head-end station 210 can dynamicallyassign the nearest WLAN access point 1600. If the determined location isoutside the building, the connection to the WLAN can be prohibited,thereby providing data security. In one embodiment, the WLAN accesspoint 1600 can also carry the UWB-IR signals.

FIG. 17 is a schematic view of an exemplary deployment of a fiber opticarray cable 336 in an indoor setting to help assist in placing andlocating emergency 911 (E911) calls. In a typical indoor cellulardistributed antenna system, E911 calls will provide information aboutthe location of the building only. In FIG. 17, one or more fiber opticarray cables 336 having multiple UWB-IR antennas 100 are deployed in theceiling of a building or other location. There are also multiplecellular repeaters 1700 in the ceiling or located elsewhere in thebuilding that provide cellular coverage. The fiber optic array cable 336employing the UWB-IR antennas 100 at the reference units 30 can be usedas discussed above with respect to FIG. 14 to determine the location ofthe user making the E911 call through the cellular network. Knowing thelocation allows more precise in-building location information whichmight not be otherwise possible with a cellular call. In one embodiment,the cellular repeaters 1700 can also carry the UWB-IR signals.

FIGS. 18A and 18B show two embodiments of the reference unit 30 of thefiber optic array cable 336.

FIG. 18A is a schematic diagram of one example of a reference unit 30connected to a fiber optic array cable 336 that comprises two separateantennas 100A and 100B. The reference unit 30 has an E/O converter 60that receives an electrical signal from one of a pair of optical fibersand converts it to an optical signal. The optical signal is thenprovided to one of the two UWB antennas 100A for the transmission of aUWB-IR signal to be transmitted. The reference unit 30 has the secondantenna 100B to receive a signal back from the OTT, and an O/E converter62 that converts the received signal to an electrical signal that istransmitted over the other fiber pair.

FIG. 18B is a schematic diagram of one example of a reference unit 30connected to a fiber optic array cable 336 showing one antenna 100 and aRF switch 1800. The one antenna 100 is a UWB antenna capable of bothtransmitting and receiving UWB-IR signals. The reference unit 30 alsoincludes an E/O converter 60, an O/E converter 62, and a pair of opticalfibers to receive and transmit signals.

To be able to dynamically select to which of the reference units 30 tosend the UWB signals, as discussed above with respect to FIG. 14, thecentral head-end station 210 may be implemented as shown in FIGS. 19Aand 19B. FIG. 19A is a schematic diagram of one embodiment of thecentral head-end station corresponding to one fiber optic array cable336, where the central head-end station 210 has an optical switchingsystem 1900A, which may be comprised of two 1×N optical switches in oneembodiment. The two 1×N optical switches may be used to dynamicallyselect which of the reference units 30 in a fiber optic reference arraycable 336 is selected. This exemplary embodiment requires fewer E/O/Econversions.

FIG. 19B is a schematic diagram of an alternate embodiment of a head-endstation 210 corresponding to one fiber optic array cable 336, where thecentral head-end station 210 has a single-pole N-throw RF switch 1900B.The RF switch 1900B may be used to dynamically select which of thereference units 30 in a fiber optic array cable 336 is selected. Thisembodiment requires more E/O/E conversions, but the cost of this may beoffset by the lower cost of the RF switch as compared to the opticalswitch.

In one embodiment, in which reference units 30 in different sections ofa single fiber optic array cable 336 are used for tracking objects, thecentral head-end station 210 may be implemented as shown in FIG. 20.FIG. 20 is a schematic diagram showing the details of a central head-endstation 210 that enables the use of different sections of a single fiberoptic array cable 336 for three-dimensional tracking of objects. Forexample, as discussed above with respect to FIG. 14, four referenceunits 30 in a single fiber optic array cable 336 may be selected totrack the location of an object. An optical switching system 2000, whichmay be comprised of two 2×N switches in one embodiment, is used toaddress each of the four reference units 30. The two 2×N switches may bereplaced by a RF switch, as shown in FIG. 19B.

In another embodiment, when some of the reference units on the fiberoptic array cables 336 are used for tracking objects, and otherreference units 30 are used for providing other wireless services, asshown above in FIGS. 15-17, the central head-end station 210 may beimplemented as shown in FIG. 21. FIG. 21 is a schematic diagram showingthe details of a central head-end station 210 that enables multipleservices to be supported by a single fiber optic array cable 336. Anoptical switching system 2100, which may be comprised of two 2×N opticalswitches in one embodiment, is used to implement the UWB-IR service, aswell as the other wireless service. An RF switch may be used in theplace of the two 2×N optical switches, as shown in FIG. 19B.

The capability of the central head-end station 210 to dynamically selectthe reference units 30 by activating the optical switch or RF switchenables the enhanced three-dimensional location tracking of an object byusing four or more reference units 30. The capability of the centralhead-end station to dynamically select the reference units 30 byactivating the optical switch or RF switch also enables the simultaneoustracking of multiple objects using the same fiber optic array cable 336installation, as well as simultaneously providing both location trackingand other wireless services.

Further, as used herein, it is intended that terms “fiber optic cables”and/or “optical fibers” include all types of single mode and multi-modelight waveguides, including one or more bare optical fibers, loose-tubeoptical fibers, tight-buffered optical fibers, ribbonized opticalfibers, bend-insensitive optical fibers, or any other expedient of amedium for transmitting light signals. Many modifications and otherembodiments set forth herein will come to mind to one skilled in the artto which the embodiments pertain having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.

Therefore, it is to be understood that the description and claims arenot to be limited to the specific embodiments disclosed and thatmodifications and other embodiments are intended to be included withinthe scope of the appended claims. It is intended that the embodimentscover the modifications and variations of the embodiments provided theycome within the scope of the appended claims and their equivalents.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

What is claimed is:
 1. An optical-fiber-based wireless communicationsystem, comprising: at least one service unit configured to receivesignals from at least one outside network; and a plurality of fiberoptic array cables configured to provide signals to the service unit,each fiber optic array cable having multiple reference units disposedalong a length of the fiber optic array cable, each of the multiplereference units containing at least one antenna, anelectrical-to-optical (E/O) converter, and an optical-to-electrical(O/E) converter, wherein the at least one service unit is configured to:cause a radio frequency (RF) signal to be transmitted from one or moreof the at least one antennas in the multiple reference units to form awireless coverage area associated with the reference unit; receive acorresponding signal from at least three of the multiple reference unitsindicative of a distance between each of the respective reference unitsand an object in the wireless coverage areas associated with therespective reference units; and process the corresponding signalsreceived from the plurality of the multiple reference units to determinea location of the object in at least two dimensions.
 2. The system ofclaim 1, wherein the RF signal transmitted from the one or more antennasis an ultrawideband (UWB) signal at a frequency between 3.1 and 10.6GHz.
 3. The system of claim 1, wherein the at least one service unit isconfigured to receive corresponding signals from at least four of thereference units and to process the corresponding signals to determine athree-dimensional location of the object.
 4. The system of claim 3,wherein the corresponding signals are received from at least fourreference units in a single one of the fiber optic array cables.
 5. Thesystem of claim 3, wherein the corresponding signals are received fromone reference unit in each of four of the multiple fiber optic arraycables.
 6. The system of claim 1, further comprising a switch configuredto dynamically select a combination of reference units to be used inobtaining the corresponding signals used to determine the location ofthe object.
 7. The system of claim 6, further comprising at least onepower line extending to the E/O converters and the O/E converters. 8.The system of claim 1, further comprising a switch configured todynamically select a combination of reference units to simultaneouslytrack the location of multiple objects.
 9. The system of claim 8,further comprising at least one power line extending to the E/Oconverters and the O/E converters.
 10. The system of claim 1, furthercomprising a switch configured to dynamically select a combination ofreference units to simultaneously track the location of the object andto provide another wireless service.
 11. The system of claim 10, furthercomprising at least one power line extending to the E/O converters andthe O/E converters.
 12. A fiber optic array cable, comprising: at leastone electrical power line; a plurality of optical fibers; and at leastfour reference units disposed along a length of the fiber optic cable,and each containing at least one antenna, an electrical-to-optical (E/O)converter, and an optical-to-electrical (O/E) converter, wherein each ofthe at least one antenna associated with each of the reference units isconfigured to: transmit a radio frequency (RF) signal to respectivewireless coverage areas associated with the respective reference units;and receive a corresponding signal from an object in the correspondingwireless coverage area, wherein the corresponding signals received at aplurality of the reference units are used to determine a location of theobject.
 13. The fiber optic array cable of claim 12, wherein at leastthree of the reference units are configured to receive correspondingsignals from the object and the corresponding signals are used todetermine a two-dimensional location of the object.
 14. The fiber opticarray cable of claim 13, wherein one or more of the reference unitscontains two antennas.
 15. The fiber optic array cable of claim 14,wherein the RF signal transmitted from the one or more antennas is anultrawideband (UWB) signal.
 16. The fiber optic array cable of claim 15,wherein the UWB signal is transmitted at a frequency between 3.1 and10.6 GHz.
 17. The fiber optic array cable of claim 15, wherein four ofthe at least four reference units are configured to receivecorresponding signals from the object and the corresponding signals areused to determine a three-dimensional location of the object.
 18. Thefiber optic array cable of claim 17, wherein one or more of thereference units contains an RF switch.
 19. The fiber optic array cableof claim 13, wherein one or more of the reference units contains oneantenna and an RF switch.
 20. The fiber optic array cable of claim 13,wherein one or more of the reference units contains two antennas and anRF switch.